The invention relates to a backing material for medical purposes, preferably for orthopaedic dressings and bandages, which is coated on at least one side and at least partially with a hotmelt adhesive composition.
As backing materials for these purposes, numerous materials based on films, wovens, knits, nonwovens, gels or foams have already been disclosed and are also employed in practice. The materials, which are often coated with a self-adhesive composition as well, are required to be skin-compatible, generally permeable to air and water vapour, and also easy to model and conformable. Based on these requirements, a very thin or soft backing is frequently preferred. For handling and in use, however, the backing materials are also required to be of sufficient strength and possibly of limited extensibility. Furthermore, the backing material should retain sufficient strength and low extensibility even after becoming wet through.
Thin backings, especially those made of nonwovens, are highly permeable to air and water vapour. For certain applications, however, their strength is too low and their extension too high.
Specific applications, an example being tapes for functional tape dressings for the prophylaxis and therapy of injuries, disorders and altered states of the musculoskeletal system, require inelastic backings having high strength in the direction of stress. This is achieved by using woven fabrics, usually of cotton or viscose. Backing materials of this kind, with appropriately high basis weight, are generally cost-intensive. High flexibility can only be achieved by means of a woven fabric of relatively low strength. When such a fabric is stressed, however, it generally exhibits a certain degree of extension, which is undesirable for its use.
When these dressings become wet through, they generally lose strength or become more extensible. This is likewise undesirable for their use and has to date been compensated by more frequent changing of dressings, which, however, is cost-intensive.
Lamination with reinforcement threads has also been disclosed in the prior art by German Patent 571 244, although the reinforcement threads employed therein are not of high tenacity. The document, then, generally gives no indication of an inelastic backing.
In addition, AU 73555/74 describes by way of example a glass filament-reinforced backing material for medical application based on foam. The backing material described here, however, is elastic or at least plastically deformable.
U.S. Pat. No. 4,668,563 describes a glass fibre-reinforced material which, however, is elastic.
Furthermore, reinforcements are not unknown in the packaging sector.
Highly adhesive orthopaedic bandages and other medical products are usually coated over the whole of their area with a zinc-rubber adhesive composition. The sticking of such products to the skin entails, following their removal, marked skin irritation and mechanical stressing of the skin. Without recourse to auxiliary means, the bond cannot be detached without pain.
In some cases there are allergic reactions. Furthermore, the adhesive compositions used often lead to a transfer of composition onto the skin.
The use of skin-friendly adhesive compositions, such as acrylate adhesive compositions, is out of the question because of their low shear stability and finger tack. Improvement through aftertreatment, especially crosslinking, is possible, although the result remains unsatisfactory overall. In addition, the bond strength to the backing of such systems, in the case of multi-ply dressings applied in circular form, is inadequate for a stable functional dressing. The proprioreceptive effect is less than that of systems with a zinc-rubber adhesive composition.
Other known adhesive systems based on conventional block copolymers are not skin-friendly, owing to the high level of added stabilizer, or because of the high cohesiveness have been found suitable to date only for industrial application; or alternatively, they cannot be formulated for strong skin adhesion and sticking to the skin.
The abovementioned adhesive compositions are pressure-sensitive self-adhesive compositions, where the compositions may be present in a carrier matrix for the purpose of processing. The term carrier matrix is understood to refer to common inorganic or organic solvents or dispersion media.
Systems without a carrier matrix are referred to as 100% systems and are likewise not unknown. They are processed in the elastic or thermoplastic state. A common mode of processing is that of the melt.
Pressure-sensitive hotmelt adhesive compositions of this kind have also already been described in the prior art. They are based on natural or synthetic rubbers and/or other synthetic polymers.
Because of their high level of hardness, sticking to the skin is a problem for such 100% systems.
An advantage of 100% systems is that they avoid an operation of removing the carrier matrix, i.e. the auxiliary media, thereby raising the productivity of processing and at the same time reducing the expenditure on machinery and the energy costs. In addition, this reduces the occurrence of residues of the carrier matrix. This, in turn, favours a reduction in the allergenic potential.
It is also known to apply such self-adhesive compositions not only over the entire area but also in the form of a pattern of dots, for example by screen printing (DE P 42 37 252 C), in which case the dots of adhesive can also differ in their size and/or distribution (EP 0 353 972 B), or by intaglio printing, in lines which interconnect in the longitudinal and transverse direction (DE P 43 08 649 C).
The advantage of the patterned application is that the adhesive materials, given an appropriately porous backing material, are permeable to air and water vapour and, in general, are readily redetachable.
A disadvantage of these products, however, is that if the area covered by the adhesive film, which per se is impermeable, is too large there is a corresponding reduction in the permeability to air and water vapour, and the consumption of adhesive composition rises, and also, if the area covered by the adhesive film is too small, the adhesion properties suffer, i.e. the product is detached too readily from the substrate, especially in the case of heavy, textile backing materials.
The object of the invention, therefore, was to develop a backing material which meets the requirements of tensile strength and also elongation at break and durability and which, moreover, avoids the disadvantages of conventional adhesive systems as described in the prior art.
This object is achieved by adding high-strength fibres, multi-strand yarns, mixed multistrands or filamentsxe2x80x94made of either an organicxe2x80x94or an inorganic-based materialxe2x80x94having an ultimate tensile stress strength of at least 60 cN/tex, preferably from 80 to 500 cN/tex, to the essentially inelastic backing materials, the high-strength fibres, multi-strand yarns, mixed multistrands or filaments exhibiting a water absorption of less than 10%, preferably less than 5% and, with particular preference, less than 3%, and the high-strength fibres, multi-strand yarns, mixed multistrands or filaments giving the backing material an ultimate tensile stress strength of at least 50 N/cm, preferably from 60 to 450 N/cm and, with particular preference, from 65 to 250 N/cm.
In addition, the backing material is at least partially coated on at least one side with a pressure-sensitive hotmelt adhesive composition.
The backing material has preferably an extension of less than 10% at a load of 10 N/cm and also preferably a basis weight of less than 350 g/m2, preferably less than 200 g/m2.
Also preferably, the backing material has an ultimate tensile stress elongation of less than 25%, preferably less than 15% and, with particular preference, less than 10%.
The backing material may have been reinforced with one or more monofil, multifil, staple spun fibre yarns and/or with oriented high-strength fibres.
In addition it is also possible to employ multi-strand yarns or mixed multistrands, especially Sirospun yarns. For specific application, single- or multi-strand fibre blend yarns may also be employed. These may comprise, for example, core-spun yarns or special staple fibre core-spun yarns.
An advantage here is that combining high-strength reinforcements and base materials it is possible to achieve particular properties or specific properties in the reinforcement thread. Examples of this are the combinations of glass or carbon and cotton or staple viscose rayon.
The fibres or filaments here can consist of organic or inorganic materials: for example, and preferably, glass, carbon or specific polyamides, and the reinforcement fibres may also have been at least partly colored in order to render the backing material more visually appealing. In this way it is readily possible to differentiate visually the reinforced backing. Colored glass or polymer filaments are particularly suitable for this purpose.
Advantageously, the orientation of the reinforcement filaments or fibres is in accordance with the stress on the backing material in use.
The backing material is also preferably laminated with the filaments and/or high-strength fibres. The filaments and/or the high-strength fibres should be firmly connected to the backing material. This can be done by direct incorporation or embedding of the fibres, filaments or multi-strand yarns, including mixed multistrands, into the backing, such as by weaving them in in the case of wovens, knitting them in in the case of knits, or embedding or inserting them in the case of the preparation process of films, gels or foams and nonwovens.
Alternatively, the fibres or the high-strength filaments can be connected to the backing subsequently, examples being welding or lamination with a corresponding connecting layer. One method appropriate for this purpose is to lay them into the film of adhesive composition.
In one advantageous embodiment the backing material attains through the addition of high-strength fibres or filaments an ultimate tensile stress strength of more than 60 cN/tex, an ultimate tensile stress strength of more than 50 N/cm and an ultimate tensile stress elongation of less than 25% with a basis weight of less than 140 g/m2. A backing material of this kind is particularly suitable for acting as the backing for a tape strip.
Preferably, in addition, at a load of 30N/cm the backing material can after 50 cycles be deformed by less than 20%, preferably 10% and, with particular preference, less than 5%.
Preferably, in addition, the backing material can be torn by hand perpendicular to the orientation of the reinforcement and/or in the direction of the reinforcement.
In addition, the backing material may also have been pretreated.
The number of attached or introduced filaments or high-strength fibres depends primarily on the particular intended use and on the desired ultimate tensile stress strength and ultimate tensile stress elongation of the backing material, on its inherent nature and on the respective strength of the fibres and filaments themselves, and can therefore be varied within relatively wide limits.
With increasing reinforcement, the backing withstands greater stress and loading. Even very highly reinforced backing materials are able to absorb or allow the passage of large amounts of moisture, and hence provide a pleasant sensation to the user.
In addition, the reinforcements are preferably inserted specifically in accordance with the direction of stress of the backing material, i.e. in the longitudinal direction. If more appropriate, however, they can also extend only or additionally in the transverse or oblique direction or, for example, in curved, spiral or zigzag formation, or randomly. In this context it may be desirable and possible to provide for the backing material to be tearable by hand perpendicular to the orientation of the reinforcement and/or in the direction of the orientation.